U.S. patent number 4,496,620 [Application Number 06/555,254] was granted by the patent office on 1985-01-29 for opaque oriented non-thermoplastic polymer film and method of forming same.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Charles R. Ashcraft, Hee C. Park.
United States Patent |
4,496,620 |
Park , et al. |
January 29, 1985 |
Opaque oriented non-thermoplastic polymer film and method of
forming same
Abstract
An opaque oriented non-thermoplastic polymer film containing
opacifying voids which opacifying voids contain rigid microspheres
therein. The method of preparing such an opaque oriented
non-thermoplastic film by incorporating rigid microspheres within
the non-thermoplastic polymer forming a film thereof and orienting
the same to create opacifying voids therein.
Inventors: |
Park; Hee C. (Fairport, NY),
Ashcraft; Charles R. (Victor, NY) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
|
Family
ID: |
24216582 |
Appl.
No.: |
06/555,254 |
Filed: |
November 25, 1983 |
Current U.S.
Class: |
428/323; 428/325;
428/328; 428/500; 156/229; 264/210.7; 428/327; 428/338;
428/910 |
Current CPC
Class: |
C08J
5/18 (20130101); B29K 2007/00 (20130101); B29K
2027/06 (20130101); B29K 2033/20 (20130101); B29K
2105/16 (20130101); B29L 2007/00 (20130101); Y10T
428/256 (20150115); B29C 48/08 (20190201); Y10T
428/25 (20150115); Y10T 428/31855 (20150401); Y10T
428/268 (20150115); Y10T 428/254 (20150115); Y10T
428/252 (20150115); Y10S 428/91 (20130101) |
Current International
Class: |
B29C
47/00 (20060101); C08J 5/18 (20060101); B32B
003/26 (); B32B 007/02 () |
Field of
Search: |
;156/229 ;264/210.7
;428/323,325,327,328,338,500,910 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Balen; William J.
Attorney, Agent or Firm: McKillop; Alexander J. Gilman;
Michael G. O'Sullivan; James P.
Claims
What is claimed is:
1. An opaque, oriented non-thermoplastic polymer film containing a
strata of voids therein, positioned at least substantially within
at least a substantial number of said voids, is at least one at
least generally spherical void-initiating, solid particle which is
phase-distinct and incompatible with said polymer, the void
occupied by said particle being substantially less than the volume
of said void, with one generally cross-sectional dimension of said
particle at least approximately a corresponding cross-sectional
dimension of said void, the population of voids in said film being
such as to cause opacity.
2. The film of claim 1 wherein said non-thermoplastic polymer is a
member selected from the group consisting of polyvinyl alcohol and
polyacrylonitrile.
3. The film of claim 2 wherein said spherical particles have a
particle size ranging from about 0.1-10 microns.
4. The film of claim 3 wherein said spherical particles are
inorganic or organic.
5. The film of claim 4 wherein said spheres are present in from 2
to 30% by weight based on the weight of said film.
6. The film of claim 5 wherein the resin, the spheres or both
contain coloring pigments.
7. The film of claim 3 wherein said non-thermoplastic resin is
polyvinyl alcohol.
8. The film of claim 3 wherein said non-thermoplastic resin is
polyacrylonitrile.
9. The structure of claim 1 wherein said voids have a dimension of
X, Y and Z, wherein dimensions X and Y are major dimensions and
dimension Z is a minor dimension at least generally corresponding
to the diameter of said spherical particle.
10. The structure of claim 4 wherein dimensions X and Y are
multiples of dimension Z.
11. The method of preparing an opaque, oriented, non-thermoplastic
film comprising:
uniformly dispersing rigid microspheres within an orientable
non-thermoplastic polymer said microspheres being at least
substantially non-adherent to said polymer,
forming a water-containing film of the microspheres-containing
polymer; and
biaxially stretching said film so as to form a strata of opacifying
voids therein.
12. The method of claim 11 wherein said polymer is a member
selected from the group consisting of polyvinyl alcohol and
polyacrylonitrile.
13. The method of claim 12 wherein said polymer is polyvinyl
alcohol and said water is the residue of an amount permitting
formation of the polymer in film form.
14. The method of claim 13 wherein said film contains from about
10-20% by weight water content before stretching.
15. The method of claim 12 wherein said polymer is
polyacrylonitrile and the microspheres-containing polyacrylonitrile
dispersion is initially formed into a dimethyl sulfoxide containing
film which is thereafter treated with water to at least
substantially exchange said dimethyl sulfoxide therein with water
to form said water-containing film.
16. The method of claim 15 wherein said water-containing film is
biaxially stretched and while in said condition, dried to
substantially remove water therefrom.
Description
The present invention is concerned with an opaque oriented
non-thermoplastic polymer film structure and to a method of forming
said film structure.
It is known that opaque, thermoplastic films can be prepared by
incorporating microspheres within said polymer, forming said
polymer into a film by coextruding the same with a skin film
thereon and biaxially orienting this structure to form in the
central core layer a strata of opacifying voids. This technique is
disclosed in U.S. Pat. No. 4,377,616, the disclosure of which is in
its entirety incorporated herein by reference. This technique is
limited to the formation of thermoplastic opaque films having
non-void containing skin films which prevent the foulling of
orientation equipment by the central core layer.
Certain polymers which can be classified as non-thermoplastic have
excellent utility in film form as barrier layers which, for
example, will not permit the transmission of oxygen or other gases
to any substantial degree. Such films find use in food packaging to
exclude the deleterious affects of air. Polyacrylonitrile film such
as that formed by the process described in U.S. Pat. No. 4,066,731
is such a film. This patent is in its entirety incorporated herein
by reference. Another such film is polyvinyl alcohol, such as that
prepared by the technique described in U.S. Pat. No. 3,985,849, the
disclosure of which is in its entirety incorporated herein by
reference. It is an object of the present invention to improve
these already excellent films by imparting an attractive opacity
and increased flex life thereto without detracting from the
outstanding gas vapor barrier characteristics of the films of this
type.
SUMMARY OF THE INVENTION
The film structure of the present invention is an opaque, biaxially
oriented non-thermoplastic film containing a strata of voids
therein. Positioned at least substantially within at least a
substantial number of said voids is at least one, at least
generally spherical void initiating solid particle incompatible
with said polymer. The void-space occupied by said particle being
substantially less than the volume of said void, with one generally
cross-sectional dimension of said particle at least approximating a
corresponding cross-sectional dimension of said void. The
population of voids in said film being such as to cause opacity in
said film.
The process for preparing a film structure of this type comprises
combining rigid microspheres with a biaxially orientable,
non-thermoplastic polymer, said microspheres being at least
substantially non-adherent to said polymer, forming a
water-containing film of the microspheres-containing polymer; and
biaxially stretching said film so as to form a strata of opacifying
voids therein.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention brings to the technology
relating to non-thermoplastic polymer films a new dimension
involving appearance and other beneficial physical characteristics
which stem from the creation of the strata of opacifying voids
processed into the non-thermoplastic polymer films. Such films are
believed to be heitherto unknown and the presence of the strata of
voids impart flexibility characteristics not present in the
non-voided film.
As employed herein the term "non-thermoplastic polymer" obviously
excludes those which can be readily brought to a melt flow
condition by the application of heat. The phrase is intended to
include those polymers which can be formed into a film by forming a
solution or plastisol thereof with a suitable solvent or liquid. In
addition these non-thermoplastic polymers in film form must be
capable of being oriented in both orientation directions either
before or after the solvent or liquid is removed from the film. As
indicated above, non-limiting examples of the broadly contemplated
non-thermoplastic polymers are polyvinyl alcohol and
polyacrylonitrile, PAN, homopolymer. A satisfactory polyvinyl
alcohol is one having a degree of polymerization of about 700 to
2,100, having a degree of hydrolysis of not less than 98% by mole
and preferably not less than 99% by mole and an average molecular
weight ranging from about 45,000 to 88,000. Conventional
plasticizers, for example, polyhydric alcohols such as glycerine,
can be incorporated into the resin. A polyvinyl alcohol of these
characteristics can be biaxially stretched in both machine and
transverse directions by any conventional orientation technique.
The orientation can be by the process of the above-mentioned U.S.
Pat. No. 3,985,849 or by techniques which employ a sequential
orientation of polyvinyl alcohol film. For orientation of polyvinyl
alcohol film, the water content should be from about 10-20% by
weight.
The contemplated polyacrylonitrile is that defined in U.S. Pat. No.
4,261,874, the disclosure of which is also incorporated herein in
its entirety by reference. While it is preferred that the
homopolymer of acrylonitrile be employed, it is to be understood
that copolymers of acrylonitrile may be employed when the units in
said copolymer derived from the acrylonitrile monomer are present
in an amount of at least about 85% by weight and preferably in an
amount of at least 92% by weight.
The polyacrylonitrile may be prepared in any conventional manner,
as by emulsion polymerization, suspension polymerization or
solution polymerization. During its preparation the contemplated
microspheres can be included in the system so that the starting
material will already contain the appropriate proportion of
microspheres. The same is true for the polyvinyl alcohol.
The following examples will describe an oriented film system where
the microspheres are added to the polymer water system prior to
extrusion of the same into an unoriented film.
The objects of the present invention are accomplished by providing
within the contemplated polymers in film form a uniform
distribution of microspheres. These microspheres must be present at
the time of orientation and they function to provide
void-initiation sites within the film during the process of
orientation. Optimally the microspheres should be incompatible with
or nonadherent to the polymer. Other than being totally
encapsulated by the polymer matrix, it should ideally have no
appreciable adherence to the adjacent polymer surface. Under the
forces of orientation, both in the machine direction and the
transverse direction, the polymer should be free to stretch away
from the generally spherical surface of the microsphere and, as a
result, a large void will be created about most of the
microspheres. A typical void in the film will have major dimensions
X and Y and a minor dimension Z, where dimension X is aligned with
machine direction orientation, dimension Y is aligned with
transverse direction orientation and dimension Z approximately
corresponds to the cross-sectional dimension of the spherical
particle which initiated the void.
It is preferred that the average particle size of the
void-initiating particles be from about 0.1 to about 10 microns.
These particles while preferably spherical in shape can also be
oblate or somewhat offround so long as gross irregularities are not
present. The void initiating particles can be of any solid or rigid
material. They can be hollow spheres or solid throughout. They may
be organic or inorganic, polymeric or non-polymeric. They must
maintain their dimensional integrity throughout the process. These
particles may be transparent or colored or specular. It is also to
be understood that the contemplated polymer mattrix material may
likewise contain coloring pigments dissolved or dispersed
throughout in order to impart tone or tint to the polymer matrix.
Microspherical particles which are incompatible with or nonadherent
to the contemplated polymers include spheres of nylon, silicate
glasses, polypropylene, teflon, metals such as steel, copper,
aluminum, ceramic spheres, etc. While the preferred particle size
of these spheres is from about 0.1 to about 10 microns, it is
particularly preferred that the particle size range from about 0.75
to about 2 microns. The void initiating particles can be present in
up to about 30% by weight and preferably from 2 to about 15% by
weight.
It is not important how or when the microspheres are incorporated
into the film structure so long as they are present at the time of
biaxial orientation. Thus, the microspheres can be incorporated
into the starting polymer during formation of the polymer or they
may be introduced into the system any time up to formation of the
unoriented film.
EXAMPLE 1
Polyvinyl alcohol powder having a degree of polymerization of about
1700 and a degree of hydrolysis of 99.95 mole percent is combined
with water to form a combination containing 40% by weight of water.
This combination is still ostensibly a dry powdered product. To
this combination is added microspheres of polypropylene. The
particle size of the microspheres range from 2-5 micron. The
spheres are present in from 7 weight % based upon the weight of the
polyvinyl alcohol. This combination is placed into a vented
extruder and plasticated by heating to a temperature of about
150.degree. C. taking care not to exceed the melting point of the
polypropylene spheres. After a uniform dispersion of the
microspheres is achieved, the resulting plastisol is cooled to a
range of about 95.degree.-115.degree. C. and extruded through a
slot die onto a chilled cast roll. The extruded film is
approximately 25 mils in thickness. Using a Bruckner orientation
system, the film is biaxially oriented and dried to at least
substantially eliminate the H.sub.2 O. The final water content will
be less than 3% by weight of the film. The biaxial orientation
results in a film which has been oriented 4 times in the machine
direction and 5 times in the transverse direction to yield a film
1.5 mils in thickness. The result will be a white opaque film of
attractive appearance and stiffness. None of the other physical
characteristics of the polyvinyl alcohol in film form will be
adversely affected. The film will have an increased Gelbo
flexibility. Its increased stiffness will assist machinability
during packaging.
EXAMPLE 2
Polyacrylonitrile homopolymer aquagel film is made according to
U.S. Pat. No. 4,066,731, except that 10% by weight glass spheres
based on the weight of the PAN resin, is incorporated into the
dimethyl sulfoxide-polyacrylonitrile resin solution. The average
particle size of the microspheres ranges from about 2-5 microns.
The dimethyl sulfoxide-polyacrylonitrile-glass spheres composition
is extruded onto a chill roll to yield a sheet approximately 10
mils in thickness. This film is backwashed with water in order to
at least substantially displace the dimethyl sulfoxide therein. The
approximately 10 mil thick film is longitudinally stretched about
two times on a machine direction orientor employing differential
speed rolls. The film is then stretched on a TDO tentering
apparatus for lateral stretching approximately three times. A
radiant heater bank at least substantially removes water from the
biaxially oriented film. The resulting film will be approximately
1.5 mils in thickness and be of an attractive white opaque
appearance. This film will have excellent barrier characteristics
and an improved Gelbo flexibility.
It is to be understood that films employed by the present technique
can have any additional surface coatings applied thereto in order
to facilitate its ultimate end use, for example, as a food
packaging film.
* * * * *